Prostate-specific antigen kinetics after hypofractionated stereotactic body radiotherapy for localized prostate cancer

Background: stereotac c body radiotherapy (SBRT) has emerged as an effec ve treatment for localized prostate cancer. However, prostate-specific an gen (PSA) kine cs a'er SBRT has not been well characterized. The objec ve of the current study is to analyze the rate of PSA decline and PSA nadir following hypofractonated SBRT in localized prostate cancer. Materials and Methods: From 2008 to 2014, thirty-nine pa ents newly diagnosed, localized prostate (25.6% low risk, 66.7% intermediate risk and 7.7% high risk) cancer were treated with SBRT using Cyberknife. Total dose of 36.25 Gy in 5 frac ons of 7.25 Gy were administered. No one received androgen depriva on therapy (ADT). PSA nadir and rate of change in PSA (slope) were calculated and compared. Results: With a median follow-up of 52 months (range, 13-71), the median rates of decline of PSA were -0.372, -0.211 and 0.128 ng/mL/month, respec vely, for dura ons of 1, 2 and 3 years a'er radiotherapy, respec vely. The decline of PSA was maximal in the first year and con nuously decreased for dura ons of 2 and 3 year. The median PSA nadir was 0.28 ng/mL a'er a median 33 months. There was one biochemical failure, occurring in a high risk pa ent. 5-year actuarial biochemical failure (BCF) free survival was 94.2%. Conclusion: In this report of localized prostate cancer, con nuous decrease of PSA level for dura on 1, 2 and 3 year following SBRT using Cyberknife resulted in lower PSA nadir. Also, SBRT leaded to long-term favorable BCF-free survival.